The second one was the best. It had a good story, best character development/story, and solid gameplay. ME1 tried to do too much, and didn't do anything particularly well, except for its story. The gameplay eventually grows on you, but the game itself lacks so much polish everywhere it just feels cheapened because of it. 3 was good in some ways, bad in others. Gameplay was overall a step up, but the abilities suffered in most cases. Older weapons felt worsened (Viper, Revenant and Tempest are all prime examples). Story was slightly beneath the other two, then escalated randomly (when he got pissed after Thessia), before flopping at the end (which gets better with time).